1. Technical Field
The present invention relates to bicycles, and more particularly, to a power-assisted system working with a bicycle.
2. Description of Related Art
Japan Patent Application Publication No. 2004-243920 has disclosed an power-assisted bicycle, which selectively provides auxiliary force according to the pedaling power and a rotation rate of the bicycle's driving wheel, thereby allowing a cyclist to ride the bicycle in an effort-saving manner.
However, for detecting the pedaling power, the prior-art device must have its crank equipped with a torque sensor that is usually expensive and difficult to install. Particularly, additional processing of the crank is required before installation of such a torque sensor and increases the manufacturing cost. Furthermore, in the event that pedals of the bicycle are unintentionally pedaled, the power-driven auxiliary device that detects the action of the pedals will make the bicycle perform sudden acceleration beyond a cyclist's expectation, which is a main reason of accidents.
Additionally, Japan Patent Application Publication No. 2000-168672 has disclosed another power-assisted bicycle that also selectively provides auxiliary force according to a rotation ratio of the bicycle's driving wheel (rear wheel) and pedaling rate. However, the prior-art device only provides consistent auxiliary force in spite of the shift position where the bicycle is on and is incapable of dynamically adjusting the auxiliary force according to the practical riding needs.